1. Field of the Invention
The invention generally relates to an active matrix liquid crystal device and manufacturing method using a five mask display architecture.
2. Description of Related Art
Active matrix liquid crystal devices (AMLCD) improve display quality by using thin film transistors (TFT) to drive pixel electrodes. The AMLCD is used in display portions of many high volume products such as laptops. Thus, there is great interest to improve manufacturing yields by simplifying the manufacturing processes leading to increased product reliability and reduction in product cost.
The pixel electrode in AMLCD designs usually comprises a layer of indium-tin-oxide (ITO) because the ITO is both transparent and conductive. Current AMLCD designs form a passivation layer over the ITO layer. The liquid crystal material is placed over the passivation layer and a common electrode is formed over the liquid crystal material completing the AMLCD device.
Since AMLCDs are commonly used in portable devices which have limited battery lifetimes, a new AMLCD structure is designed to reduce power consumption of the AMLCD. This structure is described in detail in the parent application Ser. No. 08/235,009. The new structure places the ITO layer above the passivation layer so that the voltage necessary to drive the pixel electrode is reduced, thus reducing the power consumption of the AMLCD.
A process for manufacturing the new AMLCD structure is more efficient than earlier methods. However, since the ITO layer is above the passivation layer, a source electrode to gate electrode connection requires etching a via hole through multiple layers of different materials. This etching process requires steps additional to that required to form the TFTs and pixel electrodes. These additional steps can be eliminated without affecting the processes required to form the TFT's and pixel electrodes. If these additional steps are eliminated, the cost of AMLCD will be reduced.